LeetCode Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

A:          a1 → a2                   ↘                     c1 → c2 → c3                   ↗            B:     b1 → b2 → b3

begin to intersect at node c1.

Notes:

• If the two linked lists have no intersection at all, return null.
• The linked lists must retain their original structure after the function returns.
• You may assume there are no cycles anywhere in the entire linked structure.
• Your code should preferably run in O(n) time and use only O(1) memory.

Credits:
Special thanks to @stellari for adding this problem and creating all test cases.

题意：找两个链的第一个公共节点

思路：首先得到两个链的长度，然后差就相当于是相差的步数了，较长的移动步数的话，那么两个链再同时走第一个节点就是公共节点了；还有哈希和暴力两种方法

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) { ListNode *pa=headA, *pb=headB;int lengthA = 0, lengthB = 0;while (pa) {pa=pa->next;lengthA++;}while (pb) {pb=pb->next;lengthB++;}if (lengthA <= lengthB) {int n = lengthB - lengthA;pa = headA;pb = headB;while(n) {pb = pb->next;n--;}} else{int n = lengthA - lengthB;pa = headA;pb = headB;while(n) {pa = pa->next;n--;}}while (pa != pb) {pa = pa->next;pb = pb->next;}return pa;    }};